1. Field of the Invention
The present invention relates to an optical time domain reflectometer and, more particularly, to an optical time domain reflectometer which detects backscattered light and Fresnel reflection light, generated by an optical pulse sent to a target optical fiber and returning from the fiber, to thereby automatically measure defect locations of the target optical fiber, such as the optical loss and damaged sections of the fiber in question.
2. Description of the Related Art
Optical time domain reflectometers are known apparatuses which detect backscattered light and Fresnel reflection light generated by an optical pulse sent to a target optical fiber and returning from the fiber, and perform a predetermined calculation with the detection signal in order to measure the optical loss and damaged sections of the target optical fiber.
FIG. 1 is a block diagram schematically illustrating the arrangement of this type of conventional optical time domain reflectometer.
The optical time domain reflectometer illustrated by this Figure comprises a light emitting section 1, a light-path switching section 2, a light receiving section 3, a processor 4, and a display section 5. Light emitting section 1 supplies an optical pulse to a target optical fiber 6. This pulse generates backscattered light and Fresnel reflection light in the target optical fiber, which are reflected from the fiber, and are branched by light-path switching section 2 and detected by light receiving section 3. The detection signal from section 3 is sent to processor 4 where it is subjected to a predetermined signal processing. More specifically, processor 4 amplifies the level of the received detection signal and performs the sampling of the signal at a given sampling period for later A/D conversion thereof. Subsequently, processor 4 accumulates the data for each sampling point, executes a predetermined waveform processing which includes averaging and logarithm conversion, and displays the result of the signal processing on the screen of display section 5.
When using the above optical time domain reflectometer, it is normal practice to manually measure defective or damaged sections which may be found at the spliced section of target fiber 6; such damaged sections would result in undesirable deterioration of the characteristic. First, the operator observes the trace of the backscattered light and Fresnel reflection light displayed on the screen of display section 5, and then operates appropriate switches, keys, etc. provided on the front section of the operation panel of the reflectometer to move a marker on the screen to an assumed defective point. If the difference in level between markers is equal to or greater than a specified loss, the operator aligns a cursor line with the marker position on the assumed defective point on the screen and reads the displayed distance as distance data to the defective point.
According to this conventional optical time domain reflectometer, however, when one desires to find only that defective point which shows a loss equal to or greater than a predetermined level, the work required to do so results in an increase in the number of steps the operator must perform, thus necessitating a greater length of time to obtain the desired measurement. In addition, the measured values are likely to vary depending on the skill and experience of the operator conducting the operation, in which case, it may not always be possible to obtain accurate measurements.